For Captain America I would cast Mark Wahlberg. Has an excellent experience in movies (especially action) and he also sortta looks like Steve Rogers don't you think?
As for Bucky I think we should give it to Shia LeBeouf if people pick him for Robin I can certainly pick him for Bucky.
Now for Baron Zemo (which of course I think should be one of the villains because he is the cause on bucky's "death" and Captain Americas "long absence)should be played by Hugo Weaving.
The Red Skull should be played by Liam Neeson or Ralph Fienes because these guys can play as a calm yet notorious villain.
Adolf Hitler should be played by David Bamber because he also did play Hitler in Valkyrie.
Nick fury should be Gerard Butler. (Just thinking of a white Nick Fury if you don't mind). Just imagine him with an eye-patch
The Old Black Widow could be played as the zombie-killing Milla Jovovich.
I have no idea who the love interest of The Captain is but I think this actress is qualified to be the apple of Captain Americass eyes. The love one of Steve Rogers could be Jennifer Conneley. (HULK DON'T LIKE BETTY ROSS TO BE WITH SHIELD MAN!!! lol).
Now Obviously we need cameos in this movie so I propose we add...
Wolverine and Sabretooth as you-know-who and you-know-who(duh).
Sub-mariner as Zachary Quinto (the pointy eared ba$+^rd).
And the Old Human Torch as Chris Evans....just kidding lol now the Old Human Torch as Sam Worthington (the Half-human, Half-machine)
That's my Captain America cast hope you enjoyed.